Art of ascertaining the atomic structure of materials



Oct, l, 1946.e P. c. SMITH 2,408,487

ART ASCERTATNING THE ATOMIC STRUCTURE OF MATERIALS Filed Feb. 29, 1944 P0P AMP Bnvcntor I MEM T 'Perry l.

Ctorneg Patented Oct. 1, 1946 orricla:A

ART OF ASCERTAININ G THE ATOMIC STRUCTURE F MATERIALS Perry C. Smith, Moorestown, N. J., assignor to Radio Corporation of America, a corporation of Delaware Application rFebruary 29, 1944, Serial -No.524 ,42 4

y4 claims. (cl. 25o-49.5)

This invention relates to the art of ascertaining theatomic structure of materials and has special reference to the rprovision of an improved method of and means for producing, recording and interpreting diiraction patterns.

In the usual diffraction apparatus for determining the atomic structure, of materials, the electrons orother rays (e. g., X-Iays) which strike, are which emanate from, the specimen are focused upon a photographic plate or film. Properly interpreted, the spacingand intensity ofthe rings in the resulting photograpic image or pattern provide .an indication of the atomic structure of the specimen and this makes it possible to ascertain changes in the specimen material when the said material is subjected to various treatments and chemical processes.

vThe examination 3 and interpretation ofsuch photographs requires the use of a precision inf strument, such for example as a microphotometer, and can be entrusted only to the most skilled technicians..r Further, such work is very tedious and is complicated and limited not only by human frailities and mechanical inaccuracies in the measuring instrument, but also by light scattering and other undesired phenomena peculiar to the ployed.

Accordingly. the principal object of the present invention is to obviate the foregoing and other less apparent objections to present day methods of and means for producing, recording and interpreting diffraction patterns.

As will hereinafter more fully appear, the objects of the present invention are achieved by producing a diiraction ray pattern in space, then translating the rays of which the pattern is comprised into an electric current (or voltage) of a value proportionate to the intensity of said rays at diilerent points along a radius of said pattern and then plotting or otherwise recording a graph of said current as a function of said radius. The translation or conversion of the rays (of which the diffraction pattern is comprised) into an electric current is effected directly or by means of a -secondarily-emissive electrode assembly and the plotting and recording of the current may be done either manually, with the aid of a suitable meter, or automatically as by means of a facsimile recorder or analogous device. In any event, the resulting graph or curve contains all of the information required to be known in the interpretation of a diffraction pattern and may be read by an unskilled observer without the aid of additional equipment.

particular photographic emulsion em-v Certainv details of procedure and construction,

together withv other objects and' advantages willk be apparent and the invention itself will be best understood by reference to Atheti-ollowing specil cation and to the accompanying drawing,v

wherein: Figure 1 is a schematic View of an electron dif-- fraction camera embodying the invention andv including certain Vauxiliary translating and re.

cording apparatus,

Figure 2 is a graph of a diiraction pattern-produced in the camera of Fig. 1, and Y Fig. 3 is a schematic view showing the arrangement of the electrodes of the electron multiplier pick-up in the diiracticn instrument of Fig. 1..

In Fig. l of the ydrawing there is shown an electron dilraction camera, indicated generally at comprising an evacuable chamber 3 c :ontainingga'y cathode 5, a beam forming anode 1, a specimen holder 9, an .electron lens system (exemplified by an electro-magnet) l lV and a pivotedfluorescent screen orv cassette I3all,arranged inspacedarray in the order named along ,theccntralagispfztha chamber 3. The elements thusfar described may be of any conventional design (see for example U. S. Patent No. 2,275,234) and are adapted to produce a beam l5 made up of electrons diiiracted from the specimen. As is Well known to those skilled in the art, the invisible rays of which the beam l5 is comprised, are converted into a visible image of the diffraction ray pattern when the plate I3 is moved into the path of said rays or beam." In the instant case however, the screen or plate I3 is shown swung upwardly out of the path of the beam; thus, the only diraction pattern now present within the Vacuum chamber 3 exists merely in space. (Such a pattern would be invisible to an observer looking into the chamber through one of the Viewing windows or ports I1 with which the camera is provided.)

In carrying the present inventioninto effect, the evacuable chamber 3 is provided with an electronic amplifier device I 9 such for example as the electrode assembly of an electron multiplier (say an RCA type 931A), capable of converting the rays l5 of which the diffraction pattern 1s comprised into an electric current (or voltage) of a Value proportionate to the intensity of said rays. This electrode assembly I9 is mounted for movement as on a micrometer screw 2l along a radius of the beam and is provided with a mask 23 having a slot 23a therein which is arranged in register with the first multiplying stage 4| of the device. The vacuous space about the amplier I9 and in the chamber 3 is continuous; hence the face produce many other electrons;A the number.`Y

depending on the energy of the impingingelec: trons. These secondary electrons are then directed to the next dynode new electrons. This multiplyingprocess isrepeated in each successive stage (44 to 50 inclu sive) until those emitted romth'enlast dynode,

50, are collected by the anode 5I and constitute the current utilized in the output circuit;

The relative position of the amplifier I9 along the radius of thediffraction pattern; lfisfindicated uponk a scale 25 whichY is `read in conjunc= tion with a pointer 21 on the screw I9. The out` putl of the amplierl I9" isshown connected through a switch 29'to a recorder 3l which will be understood to be driven in eynchronism vwith the screw 2 I. The recorder 3| thus automatically plots av graph orcurve showing the current generated bythe amplier I9'V as a' function' of the radius of the diffraction pattern |5 Alternatively, the output of the translating' device i9 may be connected through the switch 29 to a suitableemeter33', and 'thel meter readings plotted against thelscale 251 In either event'a graphy (see Fig; 2) is obtained which showsthe' relative intensity andfspa'cing ofthe diffractionrings and thus contains allof the informationv necessary to beknown in the interpretation off av diiractiorr pattern. The ordinatev of the curve of Fig; 2and the-markings of "the sca1e`25 Fig. l, areshown calibrated in fractions ofan inch; obviously; however', they may becalibrated inAngstromunits of atomicspacing-g if desired.

53 andknock out moref From the foregoing it is apparent that the present invention provides a simple and reliable method of and means for producing recording and interpreting diffraction patterns.

I claim as my invention:

l. In combination, means for producing a diffraction ray pattern ofj'a specimen, in a plane spaced from said specimen, means mounted for movement along a radius of said pattern for converting the diffracted rays which fall along said radius'intofan electromotive force, and means for measuring'l said electromotive force as a function of said radius.

2i Incombination;V means for producing a diffraction ray pattern of a specimen in a plane spaced from said specimen, means mounted for moyementalongaradius of said pattern for convertingvthe difracted rays which fall along said radius into an electric current, and means for recording a graph of said current as a function of said'radius.

3:. Electron diiraction apparatusvcomprising anv evacuable chamberk containing means for creat@ ing'an electronbeam Aand for directing said beam upon a specimen, an electron lens for; forming the electrons diffracted fromesaidspecimen into an electron diffraction vpattermand'forprojectinginsaid evacuab'le chamber, aA secondary-electron emissive ampliermountedl forl movementN in said' piane4 alongv aradius of said diffraction pattern andiresponsivesaidv pattern towarda plane to the impress ofsaid'diiractedelectrongthereon;

means for moving saidgamplier along said radiusin said plane, and rnean's'forindicatingztliev outrput of said amplifier.

4. The invention asf'set`forth' in claiml and wherein said indicating means' isxof the recording:

type and is adapted to-,recordthe'outputof said ampliiier as a function ofthe radius ofV said/electron diffraction pattern..

PERRY." C. SMITH." 

